This invention relates in general to apparatus for high speed, automated testing and handling of electronic devices. More specifically, it relates to a system for combing and electrically isolating from one another the leads of a radial lead device just prior to and during testing.
Radial lead devices are characterized by a body and a set of leads, typically three, that extend from one side of the body in generally the same direction. While the leads are ideally parallel, some small, but significant portion of the devices will have leads that are bent so that the leads are in electrical connection with one another. When such a device is tested, it will appear to be defective, whereas in fact it is often not defective. This problem is particularly severe in the most common type of radial lead devices, namely, small signal transistors such as type TO-92. These transistors have three closely spaced, co-planar leads formed of a fine wire material that is readily bent. As a rough rule of thumb, present testing and sorting apparatus for these transistors will reject approximately 2%-5% of the transistors as defective when in fact they are not defective, but merely have leads bent into contact with one another. In present practice, these devices are rejected and discarded. Solution of the "bent lead" problem therefore offers a considerable economic advantage.
In order to test a radial lead device, a contactor assembly makes an electrical connection between a test circuit and each lead of the device via a set of contacts mounted on the assembly. A typical such contactor assembly has been manufactured and sold by the Daymarc Corp. of Waltham, Mass., under the trade designation "TO-92 contactor". Each contact is designed to make connection with one lead of the device. The connection is made with an end portion of the contact which is oriented at a right angle with respect to the body of the contact. In this prior art assembly, the two outermost contacts have an inclined or "cut away" edge that steers the leads into alignment with the contacts as the contacts are lowered onto the leads. While this steering action will properly locate leads that are not severely bent, it may drive somewhat bent leads that are previously separated into contact with one another. If the leads of a TO-92 device are already in contact, there is no known high speed, automated system that can separate the leads reliably and maintain that separation during testing.
A major difficulty in attempts to separate the leads mechanically, as by a combing action, is that the spacing between adjacent leads, particularly co-planar leads, is very close. A comb must therefore reliably penetrate a "window" between an adjacent pair of leads that, for small signal transistors, is typically 1 mm wide. Moreover, this window must be penetrated reliably and at a high speed since modern testing equipment such as Daymarc Corporation's Type 1735 radial lead tester/sorter processes these devices at throughput rates of 7,200 devices per hour. Other problems are that a successful combing system should accommodate devices with a variety of lead shapes and cross sections and it should resist abrasion by the often rough edges of the leads. The Daymarc 1735 tester/sorter has combed type TO-18 devices using a special contactor assembly that takes advantage of the triangular array of the TO-18 leads, as viewed end on, but this contactor has not worked successfully on other devices such as the type TO-92 which have co-planar leads.
It is therefore a principal object of this invention to provide a system for combing and separating radial leads prior to and during testing.
A further object is to provide a combing and separation system that repeatedly precisely locates a combing blade in the spacing between the leads.
Another object is to provide such a combing and separation system that has an uncomplicated construction and can be used on known radial lead testers that lower onto and wipe along the leads.
A further object is to provide a combing and separation system that is both highly wear resistant and readily replaced.
Still another object is to provide a contactor assembly with the foregoing advantages that can be used interchangeably with prior art contactor assemblies of this general type.